The present invention relates to vehicle brake systems operated by fluid pressure, such as air, vacuum or hydraulic brake systems. Such vehicle brake systems are employed on heavy vehicles like tractor trailers and typically are operated on pressurized air.
A conventional trailer air brake system is illustrated in U.S. Pat. No. 3,482,666 issued Dec. 9, 1969 to Case et al and consists of a brake actuator rod which is actuated longitudinally by air pressure to rotate a brake crank arm and crank rod, thereby to set or apply the vehicle brakes. Generally, a tank of pressurized air is carried by the trailer which is connected in its associated brake system to provide air pressure to hold the vehicle brakes locked whenever the trailer is parked.
A serious problem inherent with using such brake systems as parking brakes is that should loss of pressure, vacuum or the like occur the vehicle brakes fail and thus release. If the trailer is parked on even a slight incline, the hazard exists that the trailer may roll away and cause serious property damage and/or personal injury. Also, if goods are being unloaded from the parked trailer or an attempt is made to couple a motor tractor and such brake failure should occur, the danger exists that the trailer may inadvertently roll or move and thereby cause an accident.
To eliminate these dangers, chocks have been used for blocking the trailer wheels. Unfortunately, chocks are susceptible to being stolen and also to being accidentally or intentionally removed, such as by children or saboteurs.
Further, as illustrated in the below-listed U.S. patents, various prior art devices have been devised in an attempt to eliminate these dangers.
______________________________________ 3,586,138 Engle 22 June 1971 3,482,666 Case, et al. 9 December 1969 3,037,819 Sukala 5 June 1962 2,759,569 Keehn 21 August 1956 1,484,475 Crown 19 February 1924 1,254,246 Liedloff 22 January 1918 710,522 Sauvage 7 October 1902 ______________________________________
Many of these prior art locking devices employ canting rings or plates which have a hole formed therein through which is extended the brake actuator rod. With the canting ring positioned normal to the brake actuator rod, the rod is free to move longitudinally back and forth to actuate the vehicle brakes. Once, however, the canting ring is selectively tilted away from this normal position, the sides of its hole will bind upon the actuator rod and lock it in a fixed position.
Thus, it is apparent that in brake systems employing canting rings and plates as rod locking devices it is essential that the normal positioned relationship between the canting ring and actuator rod be maintained at all times except when it is desired to lock the rod in a fixed position.
Accordingly, another and related problem with prior art air brake systems of the type disclosed in U.S. Pat. No. 3,482,666 is that upon actuation of the brake actuator rod the link or other linkage mechanism conventionally used to connect the actuator rod to the brake crank arm tends to force the actuator rod away from its longitudinal path of movement. This has two distinct disadvantages. Firstly, the link is continuously subjected to forces which may ultimately cause it to break. Secondly, if a locking device incorporating a canting ring is associated with the brake actuator rod, the actuator rod may be forced out of the normal positional relationship with the canting ring and undesirably lock up by binding therewith. Further, with trailers and like vehicles it has been found difficult to construct guide structure for restraining movement of the brake actuator rod to its selected longitudinal path of travel since such structure would have to be mounted on the wheel axle. The wheel axle of a trailer is an unsuitable location for mounting such guide structure since the axles are generally mounted on springs and thus subjected to torsional and other forces during rolling movement of the trailer.